/*
 * Copyright (C) 2014 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.util.concurrent;

import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static com.google.common.util.concurrent.MoreExecutors.newDirectExecutorService;

import com.google.caliper.AfterExperiment;
import com.google.caliper.BeforeExperiment;
import com.google.caliper.Benchmark;
import com.google.caliper.Param;
import com.google.caliper.api.Footprint;
import com.google.caliper.api.VmOptions;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.Executor;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * A benchmark comparing the {@link MoreExecutors#newDirectExecutorService()} to {@link
 * MoreExecutors#directExecutor}.
 */
@VmOptions({"-Xms12g", "-Xmx12g", "-d64"})
public class MoreExecutorsDirectExecutorBenchmark
{
    enum Impl
    {
        EXECUTOR_SERVICE
                {
                    @Override
                    Executor executor()
                    {
                        return newDirectExecutorService();
                    }
                },
        EXECUTOR
                {
                    @Override
                    Executor executor()
                    {
                        return directExecutor();
                    }
                };

        abstract Executor executor();
    }

    @Param
    Impl impl;
    Executor executor;

    static final class CountingRunnable implements Runnable
    {
        AtomicInteger integer = new AtomicInteger();

        @Override
        public void run()
        {
            integer.incrementAndGet();
        }
    }

    CountingRunnable countingRunnable = new CountingRunnable();

    Set<Thread> threads = new HashSet<>();

    @BeforeExperiment
    void before()
    {
        executor = impl.executor();
        for (int i = 0; i < 4; i++)
        {
            Thread thread =
                    new Thread()
                    {
                        @Override
                        public void run()
                        {
                            CountingRunnable localRunnable = new CountingRunnable();
                            while (!isInterrupted())
                            {
                                executor.execute(localRunnable);
                            }
                            countingRunnable.integer.addAndGet(localRunnable.integer.get());
                        }
                    };
            threads.add(thread);
        }
    }

    @AfterExperiment
    void after()
    {
        for (Thread thread : threads)
        {
            thread.interrupt(); // try to get them to exit
        }
        threads.clear();
    }

    @Footprint
    Object measureSize()
    {
        return executor;
    }

    @Benchmark
    int timeUncontendedExecute(int reps)
    {
        final Executor executor = this.executor;
        final CountingRunnable countingRunnable = this.countingRunnable;
        for (int i = 0; i < reps; i++)
        {
            executor.execute(countingRunnable);
        }
        return countingRunnable.integer.get();
    }

    @Benchmark
    int timeContendedExecute(int reps)
    {
        final Executor executor = this.executor;
        for (Thread thread : threads)
        {
            if (!thread.isAlive())
            {
                thread.start();
            }
        }
        final CountingRunnable countingRunnable = this.countingRunnable;
        for (int i = 0; i < reps; i++)
        {
            executor.execute(countingRunnable);
        }
        return countingRunnable.integer.get();
    }
}
